Extracorporeal blood pumps or in vivo heart assist devices comprise various designs, including peristaltic roller pump, centrifugal pumps, axial floe pumps, pneumatic chamber pumps, and hydraulic chamber pumps. These pumps vary widely in cost and efficacy, and their uses vary from supporting a patient on a heart/lung machine to assisting the human heart as a bridge to transplant or replacing the human heart.
Recent research suggests that better cardiac perfusion is obtained with a pulsatile flow than with a constant-rate flow since the heart is a reciprocating pump and delivers a pulsatile flow. A number of designs have been developed to introduce a pulsatile component to extracorporeal circulation. These designs generally fall into two categories. The first category consists of those devices that combine a roller or centrifugal pump with an additional device that periodically compresses the tube through which the blood or cardioplegia flows. Examples of these devices include U.S. Pat. No. 4,116,589 (RISHTON) Sep. 26, 1978, and U.S. Pat. No. 6,620,121 (MCCOTTER) Sep. 16, 2003.
A second category consists of devices in which the pump itself is used to produce a pulsatile flow. In one type of pump, such as that in U.S. Pat. No. 5,702,358, the number of revolutions per minute (RPM) of a centrifugal pump is varied in a periodic fashion to achieve a roughly pulsatile flow. In U.S. Pat. No. 5,300,015 (RUNGE) Apr. 5, 1994, a type of peristaltic pump is described, which achieves a pulsatile flow. Both of these types of designs, however, are limited in their ability to produce a pulsatile flow of desired characteristics while still maintaining a desired average flow rate.
Therefore there is a need for an apparatus for extracorporeal circulation that produces a significantly pulsatile flow, while still-maintaining a user-specified average flow rate.